McCreight et al, U.S. Pat. No. 3,378,385 discloses a ceramically bonded. high alumina refractory made from a batch consisting essentially of fused alumina grain containing titania, finely divided chrome sesquioxide, and finely divided nonfused high alumina refractory material.
Davis et al, U.S. Pat. No. 3,192,058 discloses a refractory made from a mixture which may contain chrome ore, alumina and magnesia with from about 1 to 15% added finely divided, high purity Cr.sub.2 O.sub.3.
Manigault, U.S. Pat. No. 3,888,687 discloses an alumina-chrome refractory which contains tabular alumina, calcined alumina, chronic oxide, and added phosphate compound.
Manigaust, U.S. Pat. No. 3,862,845 discloses an alumina-chromic oxide refractory composition from alumina, chromic oxide, P.sub.2 O.sub.3 and magnesium oxide.
The foregoing refractory compositions, while useful in ferrous and non-ferrous industries, specifically in automotive foundry melting and holding furnaces at the slag line, have been restricted in certain applications because they exhibit poor thermal shock resistance and little or no expansion at high temperatures.
It is an object of this invention to produce an alumina-chromic oxide refractory composition with improved thermal shock resistance and increased reheat expansion at high temperatures. A specific application of the brick of the present invention is in rotary drum induction furnaces.
As the brick of this invention generally are used in contact with various molten slags and metals, it is very important that tight joints between brick be maintained. As the brick of the prior art exhibit only very slight expansion, or even slight shrinkage, when reheated to high temperatures, they must be laid up very carefully to prevent the slag or molten metal penetrating into the joints. Accordingly, it is desirable that brick used in these applications have increased reheat expansion in order to minimize the joint penetration.
It has been found that the addition of small, but effective amounts of fume silica to alumina-chromic oxide refractories produce a brick which has improved thermal shock resistance and increased reheat expansion without sacrificing the desirable properties found in present alumina-chromic oxide brick.